Present day high performance diesel engines operate at high thermal and mechanical loads. Articulated pistons have been used in present day diesel engines due to their ability to perform in these environments. Due to the inherent structure of articulated pistons, they can withstand high thermal and mechanical loads. The independent head and skirt portions of the articulated piston design are assembled to maintain a clearance therebetween. This lack of contact allows the head portion and the skirt portion to function independently from one another. For instance, the head portion is designed to withstand the high combustion pressures and temperatures incurred during the operation of the engine while the skirt portion acts as a guide for the piston in the cylinder.
Due to the high temperatures in which the articulated pistons operate, it is important that adequate cooling is provided to the ring zone, located in the head portion, to minimize excessive wear on the ring grooves and excessive carbon formation. Generally, the head portion is manufactured with a cavity located between the combustion chamber and the ring zone. The skirt portion has a trough formed therein adjacent the cavity to define an oil gallery. Cooling oil is circulated into the oil gallery by way of an injection nozzle. However, during normal operation of the piston, the amount of cooling oil may become excessive within the oil gallery. Therefore, a portion of the cooling oil tends to overflow the trough and flow toward the cylinder through the clearance space between the head and skirt portions. Unfortunately, this process increases oil consumption and wear while raising emissions levels due to the build-up of carbon deposits on the top land of the piston and in the ring grooves.
One approach in avoiding these concerns is disclosed in U.S. Pat. No. 5,070,768 issued to Victor A. M. D. Goncalves, et al., on Dec. 10, 1991. In this approach, with the piston assembled, the lower end of the head portion below the ring zone and the upper end of the skirt portion define an oil baffle designed to prevent the cooling oil from flowing from the piston toward the space between the piston and the cylinder. For example, in one embodiment, the head and skirt portions each have a notch and projection with the projection of one fitting into the notch of the other to form the baffle. Unfortunately, the baffle only serves to inhibit the flow of cooling oil from the piston toward the cylinder through the opening and does not completely eliminate the problem.
The present invention includes a method of sealing the open space between the piston and the cylinder while still allowing the articulation advantages of a two-piece piston design. The present invention provides an inexpensive and efficient method of sealing for eliminating the loss of cooling oil from the piston to the cylinder.